I’m sorry but my crystal ball is on the blink right now but I will hazard a guess.
I imagine that if the seceding states had been allowed to go their own way in peace that over time the issues causing the separation would have been resolved and that there would be close cooperation, if not complete reunion, by now between the two nations. We would also still enjoy the constitutional republic(s) we once had instead of the mercantile empire Lincoln’s war imposed on us.
I've seen that suggested but I can't understand how anyone could believe it would ever happen. What chain of events could have caused the United States give up their independents and sovereignty and voluntarily subordinate them to Great Britain again. Regardless of whether the separation was peaceful or acrimonious I just can't imagine what could ever lead to a reunification. Especially since the South would be by far the minority partner, no pun intended. Their influence in the government would be nil at the beginning.